When a fault current occurs, especially an overcurrent, or when a short-circuit or an arcing fault occurs, the current-breaking capacity and turn-off time of a power breaker are dependent on various parameters. The turn-off process is made up of the tripping time, the inherent delay and the turn-off time. The tripping time is the time from the occurrence of the variable that causes the tripping until the initiation of the tripping process, for instance, the release of a breaker latch. This is followed by the inherent delay of the circuit breaker, which is determined by the dynamic processes of the contacts of the circuit breaker as they move and open. A turn-off time of about 50 msec is expected in a circuit breaker for the higher power range (rated current up to 100 kA).
Severe injury to persons and/or material damage can result from the occurrence of an arcing fault in an electrical installation, so this should be prevented to the greatest extent possible. In order to limit such injury or damage, several measures have been proposed, of which the optimal solution is to interrupt (to extinguish) the arcing fault in a shorter time than the turn-off time of the incoming circuit breaker.
It is a known procedure to use short circuiters to interrupt arcing faults in electrical installations. Various systems that detect physical effects of the burning arc (light, sound, pressure) can be used in such an arrangement for extinguishing an arcing fault. A proven system is based on the optical detection of an arc (EP 0575 932 B1). In order to switch off the arc, various short circuiter arrangements are proposed, for example, the use of a pyrotechnically driven short circuiter (EP 1052 665 B1 or WO 200062320 A1), by means of a short-circuit to be produced by thyristors (DE 4438593 A1) or by using a vacuum interrupter (DE 4404074 A1). Such short circuiters produce a short-circuit between the phases of the electric power system, between which the arc burns, so that the arcing fault can be extinguished within a period of time shorter than 3 msec. The advantage of an arc detection and extinguishing system is obvious.
After the short circuiter has been tripped, a short-circuit current is still flowing that is interrupt by the serially connected incoming circuit breaker (after its turn-off time), as a result of which the defective electrical installation is ultimately disconnected from the electric power system. Accordingly, a system that detects and extinguishes arcing faults consists of detection means, a short circuiter and the appertaining electronic switching means.
When a “conventional” arc detection and extinguishing system is installed, a short circuiter is connected in parallel to the power breaker in such a way that additional conductor bar elements are arranged on the conductor bar connections of the power breaker, whereby the short circuiter is positioned on the ends of said elements. The attributes, particularly the cross section of the conductor bar elements, have to match those of the conductor bars with which the power breaker and the electrical installation are supplied. This means that for the—actually “passive”—short circuiter, which is only provided for the rare serious case of an arcing fault, there is a need for a considerable amount of material. For this reason, the length of the conductor bars to be used for the connection of the short circuiter has to be selected as short as possible so that the short circuiter lies at a relatively close distance from the power breaker.
The conductor bars through which load current flows and the power breaker are heated up by the current heat and acquire an elevated operating temperature. This elevated operating temperature also spreads to the short circuiter via the highly conductive connecting bars. However, short circuiters, especially those configured as pyrotechnical short circuiters, have a thermal load limit. For instance, up until now, a pyrotechnical generator must not be operated at a continuous temperature above 85° C. [185° F.]. In order to rule out a thermal load, cooling elements are clipped onto the connecting bars when the pyrotechnical short circuiters are installed. The use of cooling elements likewise constitutes an additional material requirement.